CNC or Computer Numerical Control has been used in machining operations for decades to automate machining operations that previously were performed by a manual operator. Such operations include moving a tool or workpiece in relation to each other in three dimensional space in order to perform an operation on the workpiece. CNC programming consists of generating computer commands that are passed to a machine tool that has a CNC control. The commands instruct the control on what tool paths the machine tool should take and sets various machining conditions such as the feed, or speed the tool cuts into the workpiece, and spindle speed, or the speed with which the tool rotates when cutting the workpiece.
A CNC machine is a computer-controlled machine, which employs a simple software language to control a mechanically complex machine using open- and closed-loop control mechanisms. CNC machining is divided into two main types of machining processes: milling and turning. Milling is performed by a milling machine, and involves positioning a non-rotating work-piece underneath a spindle, which removes material using a sharp, rotating cutter, called an end mill. Turning is performed by a lathe, and involves spinning a round work-piece in a machine spindle and cutting the work-piece using a non-rotating tool bit. A picture of a typical CNC Lathe is shown in FIG. 1.
The primary goals of any CNC turning operation are quality and speed. Five main factors influence the quality and speed of a turning operation: 1) Rigidity of cutting tool, 2) Sharpness of cutting tool, 3) Hardness of work-piece, 4) Speed of work-piece rotation (“spindle speed”), and 5) Amount of material removed (“feed rate”).
Turning operations are divided into two basic types: inside turning (also called “boring”) and outside turning. Outside turning can be performed using a very rigid cutter, because the size of the tool is not restricted by the diameter of the workpiece. A picture of outside turning is shown in FIG. 2. Inside turning, on the other hand, restricts tool geometry, and therefore stiffness, because the cutter must be able to fit inside the work-piece. A picture of inside turning is shown in FIG. 3.
Inside turning can be challenging to optimize, because the five main factors listed above are inter-related and achieving a productive balance often involves trial and error. A machinist typically approaches an inside turning operation with 3 out of the 5 factors defined in advance. Sharpness of cutting tool, rigidity of cutting tool, and hardness of work-piece material are typically defined during the initial setup of a turning operation. The machinist optimizes the remaining 2 factors, speed of cut and feed rate of cut, by changing software parameters in the CNC Program. This optimization is often the result of trial and error: the machinist loads a work-piece into the machine and commands the machine to execute the CNC program. The machinist then removes the work-piece and examines its quality. If the quality is unsatisfactory, the machinist will make one or more changes to the CNC program, and repeat the process until a quality part is produced.
CNC machines are a combination of mechanical hardware, computer control systems, and computer software. CNC machines are mechanically complex, and the variety and robustness of product offerings represent some of the best American mechanical engineering. Evolution of mechanical design has continued since the industrial revolution. For the most part, the control systems and software engineering are relatively simplistic by comparison. While software engineering and computers have grown exponentially in consumer and scientific markets, industrial controls for manufacturing have fallen behind and still employ the same basic algorithms developed in the 1950's and 60's. Accordingly there remains a need drive the state-of-the-art if the United States is to remain competitive in the world market for industrial manufacturing automation. There further remains a need for the evolution of closed-loop control systems for manufacturing automation for improved productivity. The present invention fills this need by providing a method and system that provides real-time control of the machining operation by measuring properties of the tool in real-time and adjusting the machining parameters in real-time.